Loss of mental abilities represents a recognized threat to the quality of life of postmenopausal women with advancing age. Most recently, several studies found that younger women with breast cancer after themotherapy and hormonal therapy had reduced mental abilities, such as the ability to remember or concentrate,compared to women who did not undergo these treatments. These studies indicate that the agents used for breast cancer treatment and preventin cause brain damage. In the previous studies, most of the women with mental deficits obtained both chemotherapy and hormonal therapy, so that it is unclear which of the two therapies caused the mental deficits. It is the goal of this study to resolve this question. Even more importantly, tens of millions of healthy women without breast cancer may soon obtain hormonal therapy to prevent future breast cancer; it is therefore extremely important to know whether these drugs cause long-lasting problems with mental abilities. This study is a first step towards and answer to these questions.